The effect of golf club inertia on the golfer–club interaction

Abstract

Golfers continually seek improvements in performance on the golf course. One approach employed by golf club manufacturers and fitters to enable these improvements is to modify the design of the golf club. However, whilst design modifications may theoretically result in desirable performance changes, practically, these may not be realised due to the complex and unpredictable interaction between the golfer and club during the swing. Currently, the scientific understanding of the golfer-club interaction is limited, yet, improving this understanding may allow for more effective golf club design and, ultimately, golfer performance in the future. Therefore, the overall aim of this thesis was to investigate the effect of modifying the inertia of the golf club on aspects of both golfer performance and swing kinematics, thus, providing new insight into how the golfer interacts with the golf club.Initially, the effect of modifying the moment of inertia (MOI) of the golf club, located about an axis at the proximal end of the golf club, on clubhead delivery and ball launch performance was investigated, whilst also assessing the test-retest reliability of changes in performance with MOI through repeat testing sessions. Modifications to MOI were achieved by positioning approximately the same magnitude of mass (50 g) at different locations inside the golf shaft, thereby maintaining the total mass of the golf club. Clubhead velocity and ball velocity both reliably decreased with an increase in golf club MOI; however, the magnitude of the decrease in both velocity variables could not be reliably quantified. Club path, dynamic loft, vertical impact location, launch angle and spin rate all significantly differed when modifying golf club MOI; however, the changes in these variables were not reliably observed across all test sessions, whilst attack angle, face angle, horizontal impact location, resultant impact location and launch direction reliably did not change with golf club MOI. Golfer wrist kinematics were identified from the literature as a key aspect of the golf swing to quantify when modifying the inertia of the golf club. The second study focused on the development of a methodology to quantify wrist kinematics during the golf swing using an optoelectronic marker-based measurement system, with the effect of modifying the wrist tracking marker set and Cardan sequence on three-dimensional wrist angles being investigated in a two-part study. A newly developed wrist marker set, which tracked the forearm segment using one proximal tracking marker, located virtually at the elbow joint centre, and two distal tracking markers, located on the medial and lateral aspects of the forearm, was found to produce the most appropriate wrist angles. When using this marker set, the angles generated during the golf swing by the XYZ (flexion/extension, radial/ulnar deviation, axial rotation) and XZY Cardan sequences were considered most appropriate. In the final study of the thesis, both the mass and MOI of the golf club were independently increased (~ 100 g and 400 kg∙cm2, respectively) and their effects on golfer performance (clubhead delivery and ball launch) and swing kinematics (pelvis, thorax and lead/trail wrist) quantified on both a group and individual basis. On a group basis, increasing the MOI of the golf club resulted in a significant reduction in clubhead velocity, ball velocity and spin rate, which appeared to primarily be a result of reduced pelvis and thorax angular velocity at, or around the time of impact. Conversely, increasing the mass of the golf club was generally found to have a small (or negligible) and non-significant effect on the performance and swing kinematic variables measured. On an individual basis, two contrasting types of swing changes emerged as a result of modifying golf club inertia, characterised by either 1) a reduction in pelvis and thorax angular velocity during the downswing and a longer downswing time or, alternatively, 2) an increase in pelvis and thorax angular velocity during the downswing, coupled with timing differences, such as an earlier release of the wrists and a shorter downswing time. The reason for the different swing changes displayed by golfers could not be ascertained, although baseline clubhead velocity appeared to discriminate between golfers who responded differently. The findings from the research conducted in this thesis are considered to have provided new insight into the golfer-club interaction and have important implications for golf club manufacturers and fitters, as well as golf’s governing bodies. Furthermore, the application and development of novel methodologies presented in this thesis can be utilised to further explore the golfer-club interaction, with several suggestions for future research presented.